Novel synthesis of some new pyridazine and pyridazino[4,5-d]pyridazine derivatives

Article abstract of DOI:10.1080/00397911003797809

Phenacyl-malononitrile derivatives 1a and b react with dimethylformamide dimethylacetal (DMFDMA) in refluxing toluene to afford the enaminones 2a and b respectively. Compounds 2a and 2b react with the hydrazine hydrate 3a and phenyl hydrazine 3b in refluxing ethanol to afford the pyridazine derivatives 5a-d, presumably via the intermediates 4. Compounds 5a-d, react with hydrazine hydrate 3a to afford the pyridazino[4,5-d]pyridazines 6a-d respectively. The pyridazines 5a and b and the pyridazino[4,5-d] pyridazines 6a and b could be oxidized into the full aromatic systems 7a and b and 8a and b respectively. Compounds 7a and b react also with hydrazine hydrate 3a to afford 8a and b respectively.

Full text of DOI:10.1080/00397911003797809

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Novel Synthesis of Some New Pyridazine
and Pyridazino[4,5-d]pyridazine
Derivatives
Fathy M. Abdelrazek a , Ahmed A. Fadda b & Akram N. Elsayed a
a Chemistry Department, Faculty of Science, Cairo University, Giza,
Egypt
b Chemistry Department, Faculty of Science, Mansoura University,
Mansoura, Egypt
Published online: 21 Mar 2011.
To cite this article: Fathy M. Abdelrazek , Ahmed A. Fadda & Akram N. Elsayed (2011): Novel
Synthesis of Some New Pyridazine and Pyridazino[4,5-d]pyridazine Derivatives, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
41:8, 1119-1126
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Synthetic Communications1, 41: 1119–1126, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911003797809
NOVEL SYNTHESIS OF SOME NEW PYRIDAZINE AND
PYRIDAZINO[4,5-d]PYRIDAZINE DERIVATIVES
Fathy M. Abdelrazek,1 Ahmed A. Fadda,2 and
Akram N. Elsayed1
1Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt
2Chemistry Department, Faculty of Science, Mansoura University,
Mansoura, Egypt
GRAPHICAL ABSTRACT
Abstract Phenacyl-malononitrile derivatives 1a and b react with dimethylformamide
dimethylacetal (DMFDMA) in refluxing toluene to afford the enaminones 2a and b respect-
ively. Compounds 2a and 2b react with the hydrazine hydrate 3a and phenyl hydrazine 3b in
refluxing ethanol to afford the pyridazine derivatives 5a–d, presumably via the intermediates
4. Compounds 5a–d, react with hydrazine hydrate 3a to afford the pyridazino[4,5-d]pyrida-
zines 6a–d respectively. The pyridazines 5a and b and the pyridazino[4,5-d] pyridazines 6a
and b could be oxidized into the full aromatic systems 7a and b and 8a and b respectively.
Compounds 7a and b react also with hydrazine hydrate 3a to afford 8a and b respectively.
Keywords Dimethylformamide-dimethylacetal; phenacyl-malononitrile; pyridazine;
pyridazino[4,5-d]pyridazine
INTRODUCTION
Pyridazine derivatives have received considerable attention in the past two
decades because of their diverse biological activities.[1,2] This class of compounds
Received January 22, 2010.
Address correspondence to Fathy M. Abdelrazek, Chemistry Department, Faculty of Science,
Cairo University, Giza, Egypt. E-mail: prof.fmrazek@gmail.com
1119

1120
F. M. ABDELRAZEK, A. A. FADDA, AND A. N. ELSAYED
Scheme 1. Synthesis of some new pyridazine and pyridazino[4,5-d]pyridazine derivatives.
is reported to show aldose-reductase inhibitory,[3] antihypertensive, anticonvulsant,
antispasmodic, and muscle relaxant effects, and inhibits blood platelet aggregation.
They are also used as antihistaminic, analgesic, anti-inflammatory, and cardiotonic
agents with vasodilator activity.[4–6] In addition, these compounds were also reported
to show herbicidal and fungicidal[7,8] activities. In the past two decades, we have been
involved in a program aiming at the synthesis of heterocyclic compounds of expected
biological activity to be tested as biodegradable agrochemicals.[9–18] In the context of
this program and because of increased interest in pyridazine derivatives, some new
pyridazine derivatives were required for biological activity studies. 2-(1-Aroyl-
2-dimethylamino-vinyl)-malononitrile compounds 2a and b[19] (Scheme 1) seemed
to be good precursors to fulfill this objective via their reaction with hydrazine and
phenyl hydrazine.
RESULTS AND DISCUSSION
Thus compounds 1a and b were prepared according to our previously reported
methods.[20,21] Compounds 1a and b were allowed to react with dimethylformamide

PYRIDAZINE AND PYRIDAZINO[4,5-d]PYRIDAZINE DERIVATIVES
1121
dimethylacetal (DMFDMA) in refluxing toluene to afford the enamines 2a and b
respectively as recently described by us.[19]
Compounds 2a and b react with hydrazine hydrate 3a and phenyl hydrazine 3b
in refluxing ethanol to afford the dihydropyridazine derivatives 5a–d respectively.
This reaction is assumed to take place via the substitution of the dimethylamine
by the hydrazines to give the intermediate 4, which undergoes in situ cyclization
to give the final isolable products 5a–d. The infrared (IR) spectra of these products
showed a cyano and a carbonyl absorption bands at tmax ꢀ 2200 and 1655 cmꢁ1
1
respectively. The H NMR spectra of these compounds show generally the pyrid-
azine H at d ꢀ 7.25 ppm and the two NH protons at d ꢀ 8.2 and 9.05 ppm in the case
of 5a and b and only one NH at d ꢀ 9.05 in the case of 5c and d with increased
aromatic proton integration by 5H.
We have explored the b-ketonitrile moiety in compounds 5a–d for further reac-
tions. Thus 5a–d were refluxed in ethanol with hydrazine hydrate 3a to afford yellow
to brown products.
The IR spectra of these products did not reveal any absorption bands that can
be attributed to cyano or carbonyl functions. Based on this, as well as the analytical
and NMR data, structures 6a–d were assigned to these products.
The dihydropyridazines 5a and b could be oxidized easily upon reflux in acetic
acid in the presence of lead acetate in an open atmosphere to afford the full aromatic
3-aminopyridazine derivatives 7a and b respectively. Under the same reaction con-
ditions, the dihydropyridazino[4,5-d]pyridazines 6a and b were successfully oxidized
to the corresponding full aromatic derivatives 8a and b. The 1H NMR spectra of 7a
and b and 8a and b were all void from the NH signals. The oxidation process perhaps
occurred by atmospheric oxygen.
Compounds 7a and b were allowed to react with hydrazine hydrate in refluxing
ethanol to afford the pyridazino[4,5-d]pyridazines 8a and b respectively. Analytical
and spectral data are in complete agreement with the assigned structures, and some
of them are substantiated with 13C NMR data.
EXPERIMENTAL
Melting points were measured on an Electrothermal (9100) apparatus and are
uncorrected. IR spectra were recorded as KBr pellets on a Perkin-Elmer 1430 spec-
trophotometer. The 1H NMR and 13C NMR spectra were taken on a Varian Gemini
300-MHz spectrometer in dimethylsulfoxide (DMSO-d6) using tetramethylsilane
(TMS) as internal standard, and chemical shifts are expressed in d ppm values. Mass
spectra (MS) were taken on a Shimadzu GCMS-GB 1000 PX instrument (70 ev).
Elemental analyses were carried out at the Micro-analytical Center at Cairo
University.
Synthesis of 3-Amino-5-aroyl-1,2-dihydro-pyridazine-4-carbonitrile
Derivatives 5a–d
Hydrazine hydrate or phenyl hydrazine (10 mmol) was added to a solution of
each of compounds 2a and b (10 mmol) in ethanol (10 ml). The reaction mixture
was refluxed for ꢀ3–5 h [thin-layer chromatography (TLC) control using ethyl

1122
F. M. ABDELRAZEK, A. A. FADDA, AND A. N. ELSAYED
acetate–petroleum ether 1:1]. The mixture was left to cool to room temperature in
each case, then poured onto ice-cold water and acidified with a few drops of HCl
until it was just neutral. The solids so formed were collected by filtration and recrys-
tallized from ethanol to give the products 5a–d.
Selected Data
3-Amino-5-benzoyl-1,2-dihydropyridazine-4-carbonitrile
5a. Yellow
product; yield 1.5 g (67%); mp 227–229 ꢂC. tmax ¼ 3410, 3332, 3065 & 2130 (NH2
& NH), 2203 (CN), 1658 (CO); dH ¼ 4.76 (br, 2H, NH2, D2O exchangeable), 7.30
(s, 1H, pyridazine H), 7.40–7.84 (m, 5H, Ar-H), 8.22 (br, 1H, NH, D2O exchange-
able), 9.10 (br, 1H, NH, D2O exchangeable); dC ¼ 99.67 (s), 109.24 (s), 118.46 (s),
124.34 (d), 129.18 (d), 129.30 (d), 149.83 (s), 160.54 (d), 166.59 (s), 192.00 (s). MS:
m=z (%) 226 (Mþ). Anal. calcd. for C12H10N4O (226.23): C, 63.71; H, 4.46; N,
24.76. Found: C, 63.55; H, 4.40; N, 24.90.
3-Amino-5-(4-methylbenzoyl)-1,2-dihydropyridazine-4-carbonitrile 5b.
Dirty yellow product; yield 1.5 g (63%); mp 213–215 ꢂC. tmax ¼ 3400, 3329, 3063 &
2132 (NH2 & NH), 2196 (CN), 1655 (CO); dH ¼ 2.3 (s, 3H, Me), 4.74 (br, 2H,
NH2, D2O exchangeable), 7.25 (s, 1H, pyridazine H), 7.28 & 7.72 (2d, 4H, Ar-H),
8.17 (br, 1H, NH, D2O exchangeable), 9.02 (br, 1H, NH, D2O exchangeable).
MS: m=z (%) 240 (Mþ). Anal. calcd. for C13H12N4O (240.26): C, 64.99; H, 5.03;
N, 23.32. Found: C, 65.05; H, 5.15; N, 23.25.
3-Amino-5-benzoyl-2-phenyl-1,2-dihydropyridazine-4-carbonitrile 5c.
Dark yellow product; yield 2 g (66%); mp 239–240 ꢂC. tmax ¼ 3408, 3330, 3068 &
2132 (NH2 & NH), 2205 (CN), 1658 (CO); dH ¼ 4.82 (br, 2H, NH2, D2O exchange-
able), 7.25 (s, 1H, pyridazine H), 6.65–7.85 (m, 10H, Ar-H), 9.05 (br, 1H, NH, D2O
exchangeable); MS: m=z (%) 302 (Mþ). Anal. calcd. for C18H14N4O (302.33): C,
71.51; H, 4.67; N, 18.53. Found: C, 71.55; H, 4.48; N, 18.65.
3-Amino-5-(4-methylbenzoyl)-2-phenyl-1,2-dihydropyridazine-4-carbo-
nitrile 5d. Dark brown powder; yield 1.9 g (62%); mp 232–234 ꢂC. tmax ¼ 3395,
3330, 3060 & 2130 (NH2 & NH), 2204 (CN), 1656 (CO); dH ¼ 2.3 (s, 3H, Me),
4.75 (br, 2H, NH2, D2O exchangeable), 7.25 (s, 1H, pyridazine H), 6.65–7.72 (m,
9H, Ar-H), 9.08 (br, 1H, NH, D2O exchangeable). MS: m=z (%) 316 (Mþ). Anal.
calcd. for C19H16N4O (316.36): C, 72.13; H, 5.10; N, 17.71. Found: C, 72.28; H,
5.15; N, 17.80.
Reaction of 3-Amino-5-aroyl-1,2-dihydro-pyridazine-4-carbonitrile
Derivatives 5a–d with Hydrazine Hydrate 3a (Preparation of 6a–d)
A mixture of each of compounds 5a–d (10 mmol) and hydrazine hydrate
(10 mmol) in ethanol (15 ml) was refluxed for 1 h. The reaction mixture was left to
cool to room temperature in each case, then poured onto ice water and acidified with
a few drops of HCl until it was just neutral. The solids so formed were collected
by filtration and recrystallized from ethanol=dimethylformamide (DMF) to give
products 6a–d.

PYRIDAZINE AND PYRIDAZINO[4,5-d]PYRIDAZINE DERIVATIVES
1123
Selected Data
5-Phenyl-2,3-dihydropyridazino[4,5-d]pyridazine-1,8-diamine 6a. Yellow
product; yield 1.5 g (63%); mp 222–223 ꢂC. tmax ¼ 3390, 3328, 3065 & 2129 (NH2 &
NH); dH ¼ 4.74 (br, 2H, NH2, D2O exchangeable), 5.14 (br, 2H, NH2, D2O
exchangeable), 6.05 (s, 1H, pyridazine H), 7.32 & 7.65 (m, 5H, Ar-H), 8.15 (br,
1H, NH, D2O exchangeable), 9.00 (br, 1H, NH, D2O exchangeable). MS: m=z (%)
240 (Mþ). Anal. calcd. for C12H12N6 (240.26): C, 59.99; H, 5.03; N, 34.98. Found:
C, 59.86; H, 5.10; N, 35.09.
5-(4-Tolyl)-2,3-dihydropyridazino[4,5-d]pyridazine-1,8-diamine
6b.
Dirty yellow product; yield 1.5 g (63%); mp 205–206 ꢂC. tmax ¼ 3392, 3330, 3065 &
2130 (NH2 & NH); dH ¼ 2.32 (s, 3H, Me), 4.75 (br, 2H, NH2, D2O exchangeable),
5.15 (br, 2H, NH2, D2O exchangeable), 6.07 (s, 1H, pyridazine H), 7.15 & 7.52
(2d, 4H, Ar-H), 8.15 (br, 1H, NH, D2O exchangeable), 9.05 (br, 1H, NH, D2O
exchangeable). MS: m=z (%) 254 (Mþ). Anal. calcd. for C13H14N6 (254.29): C,
61.40; H, 5.55; N, 33.05. Found: C, 61.32; H, 5.50; N, 33.15.
2,5-Diphenyl-2,3-dihydropyridazino[4,5-d]pyridazine-1,8-diamine
6c.
Yellowish brown product; yield 1.5 g (63%); mp 243–244 ꢂC. tmax ¼ 3392, 3329,
3067 & 2127 (NH2 & NH); dH ¼ 4.78 (br, 2H, NH2, D2O exchangeable), 5.16 (br,
2H, NH2, D2O exchangeable), 6.03 (s, 1H, pyridazine H), 7.28–7.65 (m, 10H,
Ar-H), 9.10 (br, 1H, NH, D2O exchangeable). MS: m=z (%) 316 (Mþ). Anal. calcd.
for C18H16N6 (316.36): C, 68.34; H, 5.10; N, 26.56. Found: C, 68.38; H, 5.17; N,
26.65.
2-Phenyl-5-(4-tolyl)-2,3-dihydropyridazino[4,5-d]pyridazine-1,8-diamine
6d. Coffee-brown product; yield 1.5 g (63%); mp 253–255 ꢂC. tmax ¼ 3391, 3325,
3065 & 2135 (NH2 & NH); dH ¼ 2.35 (s, 3H, Me), 4.76 (br, 2H, NH2, D2O exchange-
able), 5.18 (br, 2H, NH2, D2O exchangeable), 6.08 (s, 1H, pyridazine H), 7.25–7.62
(m, 9H, Ar-H), 9.12 (br, 1H, NH, D2O exchangeable). MS: m=z (%) 330 (Mþ). Anal.
calcd. for C19H18N6 (330.39): C, 69.07; H, 5.49; N, 25.44. Found: C, 69.0; H, 5.45; N,
25.35.
Oxidation of 5a and b and 6a and b
Lead acetate (3.25 g; 10 mmol) was added to a solution of each of 5a, 5b, 6a, or
6b (10 mmol) in glacial acetic acid (15 ml), and the reaction mixture was refluxed for
ꢀ2–3 h in each case [TLC control]. The reaction mixture was filtered off while hot to
remove any insoluble residues, and the filtrate was left to cool and then poured onto
ice-cold water. The precipitated solids, thus formed, were collected by filtration
and recrystallized from ethanol to give dark yellow products of 7a, 7b, 8a, and 8b
respectively.
Selected Data
3-Amino-5-benzoyl-pyridazine-4-carbonitrile 7a. Dirty yellow product;
yield 1.42 g (63%); mp 147–149 ꢂC. tmax ¼ 3213 & 2232 (NH2), 2215 (CN), 1655
(CO); dH ¼ 5.56 (br, 2H, NH2, D2O exchangeable), 7.55–8.10 (m, 5H, phenyl-H),

1124
F. M. ABDELRAZEK, A. A. FADDA, AND A. N. ELSAYED
8.48 (s, 1H, pyridazine 6-H). dC ¼ 100.98 (s), 111.42 (s), 121.54 (d), 126.34 (d), 129.99
(d), 143.39 (s), 154.54 (d), 158.34 (s), 176.53 (s), 191.32 (s). MS: m=z (%) 224 (Mþ).
Anal. calcd. for C12H8N4O (224.22): C, 64.28; H, 3.60; N, 24.99. Found: C, 64.35; H,
3.65; N, 25.09.
3-Amino-5-(4-methylbenzoyl)-pyridazine-4-carbonitrile 7b. Dirty yellow
product; yield 1.5 g (63%); mp 142–143 ꢂC. tmax ¼ 3329, 3218 (NH2), 2196 (CN),
1658 (CO); dH ¼ 2.3 (s, 3H, Me), 4.74 (br, 2H, NH2, D2O exchangeable), 7.28 &
7.72 (2d, 4H, Ar-H), 8.17 (s, 1H, pyridazine 6-H). MS: m=z (%) 238 (Mþ). Anal.
calcd. for C13H10N4O (238.24): C, 65.54; H, 4.23; N, 23.52. Found: C, 65.58; H,
4.45; N, 23.68.
4-Phenylpyridazino[4,5-d]pyridazine-1,8-diamine 8a. Yellow product;
yield 1.59 g (67%); mp 214–215 ꢂC. tmax ¼ 3410, 3332 (NH2); dH ¼ 7.25–7.65 (m,
5H, Ar-H), 7.92 (br, 4H, 2NH2, D2O exchangeable), 8.25 (s, 1H, pyridazine H).
MS: m=z (%) 238 (Mþ). Anal. calcd. for C12H10N6 (238.25): C, 60.50; H, 4.23; N,
35.27. Found: C, 60.56; H, 4.30; N, 35.35.
4-(4-Tolyl)-pyridazino[4,5-d]pyridazine-1,8-diamine 8b. Yellow product;
yield 1.63 g (65%); mp 212–213 ꢂC. tmax ¼ 3412, 3335 (NH2); dH ¼ 2.33 (s, 3H,
Me), 7.10–7.45 (2d, 4H, Ar-H), 7.90 (br, 4H, 2NH2, D2O exchangeable), 8.35 (s,
1H, pyridazine H). MS: m=z (%) 252 (Mþ). Anal. calcd. for C13H12N6 (252.27): C,
61.89; H, 4.79; N, 33.31. Found: C, 61.95; H, 4.87; N, 33.46.
Transformation of 7a and b into 8a and b
A mixture of each of compounds 7a or 7b (10 mmol) and hydrazine hydrate
(10 mmol) in ethanol (15 ml) was refluxed for 1 h. The reaction mixture was left to
cool to room temperature in each case, then poured onto ice-water and acidified with
a few drops of HCl until it was just neutral. The solids thus formed were collected by
filtration and recrystallized from ethanol=DMF to give products identical in all
respects with compounds 8a and 8b.
CONCLUSION
We could prepare series of substituted pyridazine and pyridazino[4,5-d]pyrid-
azine derivatives of anticipated diverse biological activities from laboratory-available
starting materials. The synthetic methods used throughout are rather simple, and no
hazardous solvents were involved.
ACKNOWLEDGMENTS
F. M. Abdelrazek thanks the Alexander von Humboldt Foundation
(Germany) for the continuous help and support through granting short research
fellowships. The kind hospitality of Professor Peter Metz, Institut fur Organische
¨
Chemie, TU Dresden, is also highly appreciated.

PYRIDAZINE AND PYRIDAZINO[4,5-d]PYRIDAZINE DERIVATIVES
1125
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